Snow - Water Equivalent
The amount of water you would get after melting snow
Every year snow falls and snow melts somewhere on the planet. When the snow falls it depends on atmospheric variables such as temperature and moisture to determine if the snow is a light, fluffy snow or a heavy, wet snow. While light and fluffy snow can add up much faster there is actually a lot more of the wet, heavy, break your back trying to shovel it type of snow.
If you have ever skied in the Sierra of California then you have experienced “Sierra Cement” as the locals may call it. This type of snow develops in a very wet, not super cold environment with moisture feeding in from the Pacific Ocean and being forced up the west side of the Sierra Mountains. Snow falls over the peaks and can add up to 100 inches (254 cm) or up to the roof level of houses. While there is some cushion if you fall in this type of snow, it packs down pretty easily and can have less give than fresh powder.
On the flip side, if you ski in Utah where there is less moisture but often colder temperatures and a steeper mountain face for the air to rise up and over then you would experience a dry, powdery snow that also can add up to 100 inches, but is super forgiving and like falling into a sea of feathers. While there is a lot of snow, this drier snow when melted will result in much less water than the heavy wet snow. This is important for people that manage drinking water, droughts, wildfires and energy.
One tool that meteorologists use is called Snow-Water Equivalent or SWE. This tool, for now and until the US government decides to get rid of it, is available through the NRCS (Natural Resource Conservation Service). This tool shows all kinds of data about snow in the US, but one variable that is important to understand is SWE % of normal. Basically you will be able to see how much water would be available if the snow was melted but as a percentage of normal for different watershed basins across the western US.
If you’ve ever wondered why there is water shortage in California, one part of your research should be about the amount of snow that occurred in the past two winters. Reservoir managers in California try to keep reservoirs near max as long as possible in the case of a low snow year and or a hot, dry summer period. If you get two consecutive years of low snow combined with hot and dry, then a drought and real water scarcity could be on tap.
The next time you hear in the news about wildfires, lack of snow, big snow storms, water shortages, flooding, or are thinking about going skiing you should remember this NRCS website as a good starting point for understanding where the snowpack is and where it has been.